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PASS Sem2 > PASS > Flashcards

PASS Flashcards

1
Q

What are the 2 types of statistics

A

Descriptive , inferential (analysed)

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2
Q

What is evidence based medicine

A

Conscientious, explicit and judicious use of current best evidence in making decisions about care of individual patients

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3
Q

What is epidemiology

A

Study of distribution and determinants of health-related states or events in specified populations and application to health problems

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4
Q

Characteristics of surveillance and descriptive studies

A

Studies distribution

One group studied, no explicit hypothesis, development of possible hypothesis

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5
Q

Analytical studies

A

Study determinants

2 or more groups
Definite hypothesis
Reject or accept

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6
Q

Experimental studies are always

A

Analytical

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7
Q

2 types of observational study

A

Descriptive and analytical

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8
Q

2 types of descriptive study

A

Ecological studies and cross-sectional surveys

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9
Q

2 types of analytical studies

A

Case-control

Cohort

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10
Q

Requirements of sample population

A

Representative, unbiased, precise

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11
Q

2 types of validity

A

Internal and external

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12
Q

What is internal validity

A

Freedom from confounding, bias or random error

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13
Q

What is external validity

A

Degree to which conclusions can be applied to the population of interest

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14
Q

2 types of error

A

Chance or bias

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15
Q

Why do chance errors happen

A

Due to sampling variation, reduces as sample size increases

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16
Q

2 types of bias

A

Selection bias or information bias

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17
Q

Reasons for selection bias

A

Study sample not representative
Group selection within study not comparable
Healthy worker effect

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18
Q

Information bias examples

A

Recall error
Observer/interviewer error
measurement error
Misclassification

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19
Q

What is prevalence

A

Absolute risk

Proportion of people with a disease

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20
Q

What is incidence

A

Absolute risk

Number of new cases within a given time frame

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21
Q

What is incidence rate ratio

A

Compares incidence rate in 2 groups

IR1/IR2 = IRR

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22
Q

What is odds ratio

A

Comparison of odds of disease in one group compared to another

Ratio of ratios

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23
Q

what is risk difference

A

Absolute risk of A - Absolute risk of B

No difference = 0

24
Q

What are person years

A

Sum of total time of everybody followed up in study

People x years

25
Q

What is 95% confidence interval

A

Range within which we can be 95% certain that the true value lies

26
Q

Wider 95% confidence interval if

A

Greater variation in population values

Smaller sample size

27
Q

How to calculate 95% confidence interval

A

Error factor = e to the power of 2 x square root of 1/a + 1/b

28
Q

What 95% confidence ratio suggests findings are not significant

A

If it spans over 1

29
Q

Upper and lower boundary calculations

A

IR x ef = upper
IR / ef = lower

Upper-lower = x

30
Q

What happens if 95% confidence interval spans over 1 e.g. 0.5-8

A

Fail to reject the null hypothesis and no statistical significance

31
Q

Issue when comparing groups

A

Confounding

32
Q

Confounding variable must influence

A

Both the group and the thing being tested

33
Q

Solutions to confounding

A

Match important confounders
Weighted average
Standardised mortality ratio

34
Q

Ecological studies key points

A

Identify groups of people to study (not individuals)
Data on group-level characteristics
Observational

35
Q

Issues with ecological studies

A 
Measurement variation 
Confounding 
Chance (random error)
36
Q

Cross-sectional survey key points

A

Survey/series of surveys
Exposure and outcome measured simultaneously
Determines prevalence mainly
Analysis of individuals

37
Q

Example of ecological study

A

Colon cancer incidence per 100,000 women and per capita daily meat consumption

38
Q

Example of cross-sectional survey

A

Effect of aircraft noise exposure on heart rate during sleep in population living near airports

39
Q

Issues with cross-sectional survey

A

Sampling bias
Responder/participant bias
Chance (random error)
Confounding

40
Q

Advantages of cross-sectional survey

A

Cheap
Fast
Reflective of real life

41
Q

Case control study key features

A 
Always retrospective 
Identify group of cases and non-cases (controls) 
Ascertain previous exposure status
Compare level of exposure in each group 
Analyse odds ratio
42
Q

What is a nested case-control study

A

Collection of data from evolving outcome and exposure database of a concurrent or prospective cohort study

43
Q

Advantages of nested case control study

A

Incidence rates calculated
Population for sampling already defined
Can collect more detailed information for a minority of participants

44
Q

Advantages for case control study

A

Good for rare diseases
Cheap
Quick
Can study multiple exposures for a single outcome

45
Q

Issues with case control study

A

Selection bias
Information bias (misclassification)
-Non-differentiated (randomly inaccurate measurement)
-Differentiated (systematic, recall bias, assessor bias, data collection errors)
Confounding
Chance (random error)

46
Q

What is a cohort study

A

Always prospective
Group individuals according to level of exposure
Select outcome free individuals
Ascertain outcomes for everyone
Compare incidence rates for each exposure group

47
Q

Analysis of cohort study

A

Odds ratio/rate ratio

Comparisons externally e.g. standardised mortality ratio or internally e.g. IRR

48
Q

Advantages of cohort study

A

Enable derailed and prospective assessment of exposure, outcomes and confounders
Studying a range of different outcomes, rare exposure, whether exposure precedes outcome, conditions that fluctuate with age

49
Q

Issues in cohort study

A 
Loss to follow up - differential loss, survivor bias
Information bias 
Confounding 
Chance (random error) 
Expensive 
Take long time 
Large and resource intensive
50
Q

Example of cohort study

A

5000 people followed up from age 55 for 10 years
2000 smokers —> 200 developed lung cancer
3000 non smokers —-> 20 developed lung cancer

51
Q

Describing a study

A 
Study design- PICO 
Population 
Intervention/exposure 
Comparison/control 
Outcome
52
Q

What is SMR

A

Standardised mortality ratio

53
Q

SMR equation

A

Observed number of deaths/ expected number of deaths

54
Q

What bias is always present

A

Sampling bias

Random error

Also somewhat confounding

55
Q

In what study is confounding highest

A

Ecological

PASS Sem2 (2 decks)

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